The Precision Design ES-71 II Lens Hood for the Canon EF 50mm f/1.4 USM Lens is primarily designed to prevent unwanted stray light from entering the lens by extending and shading the end of the lens. In addition since the end of the lens is extended you also get the added benefit of some extra protection from accidental impact. Dedicated lens hoods such as the Precision Design ES-71 II are designed to match the specific focal length of the lens it was designed for.